The present invention relates to apparatus for burnoff of hot wire resistors in an air flow rate meter used in an internal combustion chamber.
When hot wires or hot films are used in air flow rate meters in internal combustion engines, then from time to time a burnoff or glow-heating of this resistor element must be undertaken so as to burn off or forcefully remove dirt particles deposited thereon. This must be done because of the necessity for attaining measurement results which are as free of error as possible over a long period of operation. It is already known to dispose an air flow rate meter in an internal combustion engine, having a bridge circuit and a hot wire as a measuring resistor; the hot wire is held to a constant temperature by means of a control device for the electric current which precedes the bridge circuit and is burned off after the end of each operational cycle on the basis of a predefined bridge imbalance. Generally, a further resistor in the measurement bridge is associated with the hot wire in the air intake of the engine, in order to compensate for the effect of the aspirated air temperature on the measurement result.
It has proved to be desirable for this compensating resistor, as well, to be burned free of soil, at least occasionally, so that its effectiveness is maintained.